| Summary: | <p>Regulatory T cells (Tregs) are powerful modulators of immune function, and are of increasing interest as an adoptive cellular therapy for the treatment of transplant rejection. In a number of early clinical trials, polyclonal Treg therapy has demonstrated efficacy in maintaining graft function. However, optimal Treg immunotherapy should employ alloantigen-reactive, rather than polyclonally-reactive Tregs to ensure specificity against transplant alloresponses. In the first part of this study, a method was developed to expand functional human alloantigen-reactive Tregs (arTregs). These arTregs have enhanced in vitro suppressive function and harbour more potent allospecific inhibition in comparison to polyclonally-expanded Tregs. An in-depth characterisation of arTregs is presented, providing a detailed immunophenotypic analysis. In the second part of this study, the phenotypical changes in peripheral immune cells in renal transplant patients receiving Treg therapy were assessed over time using standardised flow and mass cytometry panels. Immunophenotyping provided insights into the immune status of transplant recipients after Treg infusion. In the Treg therapy group, a distinct B cell signature of elevated transitional B cell numbers was identified. Mass cytometric characterisation of the peripheral Treg compartment in patients receiving Tregs identified an enrichment of Treg functional markers with notable changes in the expression of chemokine receptors on peripheral Tregs. In the final part of this study, cellular infiltrates in protocol renal biopsies of recipients who received Treg therapy were examined by spatial profiling and compared to rejection biopsies. This identified a unique signature of B cells, Tregs, and apoptotic regulators in the biopsies from Treg-treated patients. Further analysis revealed interesting differences between the cellular infiltrates in FOXP3hi segments from cells therapy compared with rejection such as enrichment in regulatory molecules and anti-inflammatory proteins. The findings presented in this thesis demonstrate the phenotypical and molecular processes associated with stable renal allograft in patients receiving Treg therapy, which in turn may assist in understanding the mechanisms of therapeutic immune regulation and the optimal timing for immunosuppression minimisation. </p>
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